1. Field of the Invention
The instant disclosure relates to a semiconductor device; in particular, to a super junction semiconductor device.
2. Description of Related Art
In the field of medium or high voltage power semiconductor devices, the super junction has been widely integrated in power semiconductor devices. For example, super junction transistors provide a way to achieve low on-resistance (Rds-on), while maintaining a high off-state breakdown voltage (BV).
Super-junction devices include alternating P-type and N-type doped columns formed in the drift region. In the OFF-state of the MOSFET, the columns completely deplete at relatively low voltage and thus can sustain a high breakdown voltage (the columns deplete laterally, so that the entire p and n columns are depleted).
For a super-junction, the on-resistance (Rds-on) increases in direct proportion to the breakdown voltage (BV), which is a much less dramatic increase than in the conventional semiconductor structure. A super junction device may therefore have significantly lower Rds-on than a conventional MOSFET device for the same high breakdown voltage (BV) (or conversely may have a significantly higher BV than a conventional MOSFET for a given Rds-on).
A super junction device according to the prior art is disclosed, for example, in US Pub. No. 2010230745 A1. The super junction device usually includes an active region and a termination region surrounding the active region. In the OFF-state of the super junction device, the electric field is produced along vertical and horizontal directions of the termination region.
The breakdown voltage of the super junction device may be reduced due to too large electric field intensity along the horizontal direction of the termination region. Accordingly, the termination region has a length in the horizontal direction two times to fourth times greater than a thickness of the epitaxial layer. However, if the termination region has too long length in horizontal direction, the effective region ratio of the super junction device will be reduced, and the on-resistance will increase. The prior art discloses a super-junction device including a guard ring layer within the termination region to prevent the breakdown voltage from being reduced without reducing the effective region ratio. However, the guard ring layer has a complicated pattern resulting in a complex and difficult fabrication process.